1. Field of the Invention
The present invention is directed to an electromagnetic relay, and more particularly to a miniature relay having a compact electromagnet block with a high coil packing density.
2. Description of the Prior Art
A known electromagnetic relay utilizes an electromagnet block composed of a core, a pair of flanges of dielectric materials molded on opposite ends of the core, and an excitation coil wound around the core between the flanges. In order to make electrical insulation between the core and the coil while disposing the coil as many turns as possible between the flanges for increasing coil packing density, it has been a common practice to use a thin dielectric tape for wrapping around the core between the flanges. For this purpose, the tape is desired to have a width not less than a distance between the flanges so as to fully cover the entire length of the core. However, such tape is rather difficult to be put around the core without causing interference with the flanges, thereby lowering assembly efficiency. For avoiding this inconvenience, it has been proposed to use a tape of smaller width in combination with collars which is fitted on the core to cover gaps between the width ends of the tape and the adjacent flanges. The collar is in the form of plate with a slit in which the core is fit and is held in abutment with the flange, thereby defining an effective coil space between the collars. The coil is then wound on the tape over a reduced distance between the collars. Although this scheme is effective for insulation between the coil and the core, the presence of the collars reduce the coil space to thereby lower the coil packing density, in addition to increasing the number of the components with corresponding increase in the manufacturing cost.